A membrane-bound antigen of chick red cells, characteristically present before hatching and disappearing with post-hatch development, has been shown to be inducible upon leukemogenesis with avian myeloblastosis virus (AMV). Further studies are designed to investigate the following: (a) The extent to which leukemic cells undergo generalized genetic derepression. This will be investigated by monitoring changes in enzymes or structural proteins known to vary during development. (b) Species distribution of CFA (fetal and leukemic cells). (c) Cellular distribution and specificity of CFA in the chicken. Immunologic procedures used for detecting the antigen on blood cells will be extended to other organs and tissue culture cells to determine the cellular distribution and sequence of disappearance of the antigen with time. (d) Relationship between CFA and AMV. Immunological and electron microscopic procedures will be used in this determination. By use of these combined technics it may be possible to quantitate the number of surface antigen (CFA) molecules, their distribution on the membrane and the possible function of CFA as receptor site. (e) Mitochondrial DNA of chicken leukemia. Since avian myeloblastosis can be considered the correlate of chronic granulocytic leukemic of humans, it would be interesting to determine whether or not the chicken leukemia showed the mitochondrial DNA dimers present characteristically in the human leukemias. Finally, pilot studies have shown that the antiserum used to detect chicken fetal antigen also detects more than 50 percent of human leukemias. The possibility of the use of the antiserum as a sensitive reagent for detection of human leukemia will be further explored.